1. Field of the Invention
The present invention relates to a decomposable sealing device for use in pipes or boreholes, as well as a method related thereto.
2. Description of Related Art
It is well known within the oil industry that production wells have to be tested before being put into service. One of these tests involves checking whether the well can withstand the pressure at which it is to be operated during oil/gas production. If such a check is not carried out, there is a risk of fluids leaking out of the well during operation.
In order to conduct such tests, a plug device is placed down in the well to shut off the passage. A pressure is applied from the surface by means of a suitable fluid, and by checking the well over a period of time, it is possible to investigate whether the well is sufficiently leak-proof. The plug is normally mounted as a lower part of a production tubing, and lowered internally in a casing which is installed in the well beforehand.
Test plugs are placed in a specially adapted seat/housing in the tubing, and packer systems are normally employed in order to obtain an adequate seal against the surrounding inner wall of the tubing. The packers are located in a suitable groove in the inner tubing wall, forming a seal against the radially internally situated plug located in its seat.
In today's systems it is normal practice to employ test plugs which are decomposed by being blown up in the final phase of the tests in order to admit a free through-flow in the tubing.
The use of glass test plugs is well known, and this kind of material is considered highly suitable for the oil industry. It is practically inert with regard to all types of chemicals and is safe for the personnel who have to handle the plug. The glass, moreover, retains its strength at high temperatures, and it can stay in an oil well for a very long time without sustaining damage or breakdown.
The glass used in known plugs has undergone a hardening treatment, with the result that it is brittle on one side and on the other side it possesses the strength to resist the severe pressure stresses to which it is exposed.
In today's systems, a plug like that mentioned above is removed by means of an explosive charge, with the result that the glass is shattered into tiny particles, which are easily washed out of the well without leaving any potentially harmful residue. These explosive charges may be incorporated in the actual plug, or mounted outside the actual plug. The actual detonation is remotely controlled, and can be triggered from the surface of the well.
An example of a test plug made of glass, where the plug is arranged so as to be removable by means of an explosive charge, is known from NO B1 321976. The plug comprises a number of layered or stratiform ring discs of a given thickness, which are placed in abutment on top of one another. Between the different layers in the plug a shim film of plastic, felt or paper is inserted; the different glass layers may also be joined by lamination with an adhesive such as a glue. During use the plug will be mounted in a plug-receiving chamber in a pipe, where the underside of the plug rests in a seat at the bottom of the chamber.
The use is also known of solutions where the whole or parts of the plug are made of rubber, and where a section comprises a chemical which dissolves the rubber plug when the testing is completed and the plug requires to be removed. During operations from floating rigs, however, this method will be too slow and unreliable, in light of the operating costs for this kind of platform. In this case it will be impossible to predict the exact time when the plug is removed and the passage through the well opens.
The use of explosive charges for decomposing test plugs can provide a safe and calculable removal of the plug. However, in many countries extremely stringent requirements are placed on the use and import of explosives, and it is therefore desirable to provide a solution where the test plug can be removed in a controllable manner without the use of such means.